A vehicle HVAC system is used to control the comfort level, e.g., temperature and humidity, within the vehicle cabin for the vehicle occupants. HVAC systems may allow the operator to manually set various operating parameters such as the ON/OFF state of the air conditioner, a desired temperature setting, a blower speed, airflow direction, the amount of air flow at the feet, the window, etc. Other vehicle HVAC systems use minimal operator input information, e.g., an operator desired temperature setting, and the remainder of the system parameters are automatically controlled.
One of the functions of a vehicle HVAC system is to prevent fogging of the vehicle windscreen (windshield) during vehicle operation. The prevention of windscreen fogging requires an accurate determination of the relative humidity in the vehicle adjacent to the windscreen and the temperature of the windscreen itself. It is known to combine (integrate) several vehicle sensing systems into one module. For example, a vehicle rain sensor for windscreen wiper control may be mounted in a module that is mounted against the inside of the windscreen in front of the rearview mirror. It is also known to mount a humidity sensor and an ambient air temperature sensor in the rain sensor module. Also, it is known to mount other types of sensors in the rain sensor module such as a forward looking camera. Certain sensors, such as the camera sensor, may have an associated processor circuit that generates a significant amount of heat. Heat generated from any heat source, e.g., a camera processor or any other type of heat source, can affect sensed condition of other sensors within the module such as temperature and humidity sensors. This heating effect can result in an improper determination of relative humidity thereby resulting in improper control of the vehicle's HVAC system and fogging of the windscreen.